Measuring probe

ABSTRACT

A sensor, particularly for determining the oxygen content in exhaust gasses of internal combustion engines, includes sensor element which is fixed in a metallic housing and a sealing flange which is integrally formed on the housing and rests on a sealing seat which is formed on an exhaust system. The sealing flange has two ring elements which are integrally formed on the housing and each have an inclined sealing surface, a hollow space being formed between the two ring elements inside the housing.

FIELD OF THE INVENTION

The present invention relates to a sensor, particularly for determiningthe oxygen content in exhaust gasses of internal combustion engines.

BACKGROUND INFORMATION

European Patent No. EP 624 791 (corresponding to U.S. Pat. No.5,329,806) describes a gas sensor where a sensor element is fixed in atubular, metallic housing in a gas-tight manner. At its lower part, thetubular housing has a lip facing radially outward which forms a sealingflange. The gas sensor is mounted in an opening of an exhaust system,the lip sitting on a sealing seat formed in the opening. A banjo bolt isled over the housing and screwed into a thread arranged in the opening,thereby joining the lip to the exhaust system in a gas-tight manner.Problematic in this design is, however, that the pressing or upsettingof the relatively thin-walled material of the housing can producemicrocracks at the lip which can cause the leakiness of the housing.

SUMMARY OF THE INVENTION

The present invention has the advantage over the related art that thesealing flange is absolutely gas-tight, and the inclined sealingsurfaces produce an absolutely gas-tight sealing seat at the exhaustpipe. Moreover, the hollow design of the sealing flange produces aspring effect which also supports the sealing effect.

It is particularly advantageous for the inclined sealing surfaces to bedesigned in an angle between 10° and 30°, preferably of 20°. Arrangingthe sealing flange behind the sealing arrangement for the sensorelement, as viewed from the measuring gas side, has an advantageouseffect on the installation of the sensor. In this manner, the sensorelement can first be equipped with the ceramic parts of the sealingarrangement. The housing is then slipped over the sensor elementequipped with the sealing arrangement. Furthermore, it is expedient toattach a connecting piece to the exhaust pipe, the connecting piece, atthe end face, forming a sealing seat for the sealing flange.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal cross section through a sensor mounted in anexhaust pipe.

FIG. 2 shows a detailed longitudinal cross section through the housingof the sensor according to FIG. 1.

DETAILED DESCRIPTION

A sensor 10, for example, an electrochemical oxygen sensor, is mountedin an exhaust pipe 11 and has a metallic housing 13, in which a planarsensor element 15 having a section 17 on a measuring gas side and asection 18 on a connection side is arranged.

Housing 13 is a pipe element 20 which is open on both sides and has anend section 21 on connection side and an end section 22 on measuring gasside as well as an interior wall 23 and an exterior wall 24. Moreover,pipe element 20 has a radially surrounding sealing flange 25 having anupper ring element 26 with a downward inclined upper sealing surface 26a, and having a lower ring element 27 with an upward inclined lowersealing surface 27 a. The two sealing surfaces 26 a and 27 a run at anangle a of approximately 20° relative to a plane running at right anglesto the center line of pipe element 20 (FIG. 2). Sealing flange 25 havingring elements 26, 27 running toward one another is designed in such amanner that a hollow space 29 forms inside housing 13 between ringelements 26, 27. In this manner, the two ring elements 26, 27 can act asresilient legs whereby the sealing effect of sealing surfaces 26 a, 27 ais increased. In front of sealing flange 25, as viewed from themeasuring gas side, an annular surface 28 is integrally formed oninterior wall 23, the annular surface constituting a stop face for asealing arrangement 30 which will be described later. Because of thisdesign, sealing flange 25 is located behind sealing arrangement 30, asviewed form the measuring gas side and is consequently relatively faraway from exhaust pipe 11.

To form sealing flange 25, pipe element 20 is, for example, initiallyupset, a rounded bulge forming at pipe element 20 in the process. Thisbulge is subsequently processed, for example, by the manufacturingprocess of rotary kneading in such a manner that the two inclinedsealing surfaces 26 a, 27 a are formed. However, one can also conceiveother manufacturing processes by which sealing flange 25 can bemanufactured efficiently, for example, by drawing and subsequentlyupsetting.

Sealing arrangement 30 mounted in housing 13 is composed, for example,of a molded ceramic part 31 on measuring gas side, a molded ceramic part32 on connection side, and a sealing element 33 arranged in between.Molded ceramic parts 31 and 32 are composed, for example, of Al₂O₃ andeach have penetrations, which are not further described, for sensorelement 15. Sealing element 33 is composed, for example, of steatite andis inserted in a prepressed condition, having a penetration for sensorelement 15, as well. First, housing 13 is slid over sealing arrangement30 until annular surface 28 strikes against molded ceramic part 32 onconnection side. Subsequently, molded ceramic part 31 on measuring gasside is acted upon by a stamp on measuring gas side, using a pressureforce rated such that prepressed sealing element 33 is squashed so thatthe power components press both against sensor element 15 and interiorwall 23. While the force is acting upon molded ceramic part 31 onmeasuring gas side, a contraction in area 35 running radially and facinginward is formed in pipe element 20 at end section 22 on measuring gasside. In this manner, ceramic part 31 on measuring gas side is kept inthe pressing position with respect to sealing element 33.

At end section 22 on measuring gas side, sensor element 15 protrudesfrom housing 13 and is surrounded there, for example, by a doubleprotective tube 40. Double protective tube 40 is inserted into endsection 22 on measuring gas side, and there joined to housing 13 by asurrounding weld 41. Double protective tube 40 has gas entrance andoutlet apertures 41 for the exhaust gas/measuring gas. In the presentexemplary embodiment, double protective tube 40 is formed in one piece.

End section 21 on connection side of housing 13 has a tapering section45 with an opening 46. Welded in opening 46 is, for example, a metallicjacketed tube 47. Arranged in jacketed tube 47 are connecting cables 48for sensor element 15. Connecting cables 48 are connected to contactingpieces 49 which are contacted to terminals (not further shown), whichare arranged at section 18 on connection side of sensor element 15.Sensor element 15 can be contacted, for example, by clamping or by anintegral connection. However, the cables may be brought out throughopening 46 with the assistance of a temperature-resistant PTFE cablegland, as well.

For fasting sensor 10 in exhaust pipe 11, an opening 60 is provided inexhaust pipe 11, a cylindrical connecting piece 62 having a planeannular surface 63 and a threaded section 64 being welded into theopening. Lower sealing surface 27 a of sealing flange 25 rests onannular surface 63. A union nut 70 having an internal screw thread 71and an internal annular surface 72 is led over housing 13. Union nut 70is screwed on connecting piece 62, thereby pressing sealing flange 25 onannular surface 63. Thus, annular surface 63 constitutes a sealing seatfor sealing flange 25.

For fasting sensor 10 in exhaust pipe 11, however, other forms offastening means are also possible, for example, fastening with theassistance of a banjo bolt having a thread on the outer surface which isscrewed into an internal screw thread arranged on connecting piece 62,the sealing seat for sealing flange 25 having to be designed with anadditional annular surface inside connecting piece 62. It is alsoconceivable to interposition an adaptor between connecting piece 62 andthe banjo bolt, sensor 10 then, with sealing flange 25, sitting on anannular surface of the adaptor, and the adaptor, with a further annularsurface, resting on the annular surface of connecting piece 62.

What is claimed is:
 1. A sensor for determining an oxygen content in anexhaust gas of an internal combustion engine, comprising: a housing; asensor element fixed in the housing; and a sealing flange formed out ofa material of the housing, the sealing flange including two ringelements formed out of the housing, each of the two ring elements havingan inclined sealing surface, a hollow space being formed between the tworing elements inside the housing, the two ring elements acting asresilient legs.
 2. The sensor according to claim 1, wherein the sealingsurfaces are slanted at an angle of 10° to 30° relative to a planerunning at right angles to a center line of the housing, the housingbeing tubular-shaped.
 3. The sensor according to claim 2, wherein theangle is about 20°. 4.The sensor according to claim 1, furthercomprising a sealing arrangement for the sensor element mounted in thehousing, the sealing flange being situated behind the sealingarrangement, as viewed from a measuring gas side of the sensor.
 5. Thesensor according to claim 4, wherein the housing further comprises twoannular surfaces, a first of the two annular surfaces being further froma measuring gas than a second of the two annular surfaces, the sealingarrangement being pressed between the two annular surfaces.
 6. Thesensor according to claim 1, further comprising a connecting pieceencircling an opening in an exhaust pipe in a gas-tight manner, asealing seat for the sealing flange being formed on the connectingpiece.
 7. The sensor according to claim 1, further comprising afastening element for mounting the housing in an exhaust pipe. 8.Exhaust pipe for an internal combustion engine with a sensor fordetermining an oxygen content in an exhaust gas of the internalcombustion engine in the exhaust pipe, comprising: a pipe with anopening; a cylindrical connecting piece, the cylindrical connectingpiece having a plane annular section, the cylindrical connecting piecebeing welded into the opening; a housing; a sensor element fixed in thehousing; and a sealing flange formed out of a material of the housing,the sealing flange including two ring elements formed out of thehousing, each of the two ring elements having an inclined sealingsurface, a hollow space being formed between the two ring elementsinside the housing, the two ring elements acting as resilient legs; thesealing flange resting on the plane annular section of the cylindricalconnecting piece.